The human carcinoembryonic Ag (CEA)3 protein family encompasses several forms of proteins with different biochemical features. These proteins are encoded by 29 genes tandemly arranged on chromosome 19q13.2. CEA family genes have been classified into two major subfamilies, the CEA cell adhesion molecule (CEACAM) and the pregnancy-specific glycoprotein subgroups. The CEACAM proteins, which are part of the larger Ig superfamily, include CEACAM1, -3, -4, -5, -6, -7, and -8. They share a common basic structure of sequentially ordered different Ig-like domain(s) and are able to interact with each other. For example, it has been reported that various CEACAM proteins, such as CEACAM1 or CEACAM5, exhibit both homophilic and heterophilic interactions.
CEACAM1 (CD66a), a transmembrane protein and member of the carcinoembryonic Ags family, contains two ITIM sequences located within its cytosolic tail. CEACAM1 interacts with other known CD66 proteins, including CD66a, CD66c, and CD66e proteins. It is expressed on a wide spectrum of cells, ranging from epithelial to hemopoietic origin. Among CD66 proteins tested, only the CD66a protein is expressed on the surface of activated CD16-negative NK cells.
The various CEACAM proteins have different biochemical features, including but not limited to anchorage to cell surface (GPI-linked, transmembrane or secreted forms), length of cytoplasmic tail (long or short), and the presence or absence of various signal transduction motifs. These proteins are actively involved in numerous physiological and pathological processes.
CEACAM1 is a transmembrane protein that can be detected on some immune cells as well as on epithelial cells. Many different functions have been attributed to the CEACAM1 protein. It was shown that the CEACAM1 protein exhibits antiproliferative properties in carcinomas of colon, prostate, as well as other types of cancer. Additional data support the central involvement of CEACAM1 in angiogenesis and metastasis. CEACAM1 also has a role in the modulation of innate and adaptive immune responses. The present inventor has shown that CEACAM1 homophilic interactions inhibit NK-mediated killing activity independently of MHC class I recognition. This novel mechanism plays a pivotal role in the inhibition of activated decidual lymphocytes in vitro and most likely also in vivo after infection, including for example CMV infections. The CEACAM1 homophilic interactions are possibly important in some cases of metastatic melanoma, as increased CEACAM1 expression was observed on NK cells derived from some patients compared with healthy donors. There is an association of CEACAM1 expression on primary cutaneous melanoma lesions with the development of metastatic disease and poor survival. The present inventor has demonstrated the role of CEACAM1-mediated inhibition in maintaining NK self-tolerance in TAP2-deficient patients. Additional reports have indicated that CEACAM1 engagement either by TCR cross-linking with mAb or by Neisseria gonorrhoeae Opa proteins inhibits T cell activation and proliferation.
The CEACAM1 protein interacts with other CEACAM protein family members, such as CEACAM1 itself and CEACAM5. At least part or the entire binding site of human CEACAM1 is located at the N-terminal Ig-V-type domain of the CEACAM1 protein. In particular, amino acids 39V and 40D and the salt bridge between 64R and 82D may play an important role in this binding. Most amino acid sequences of the N-terminal domain of CEACAM1, -3, -5, and -6 are identical, and predicted binding residues are conserved among the four proteins. These proteins might interact with each other. This is of particular importance, because in certain tumors the CEACAM1 protein is down-regulated, followed by upregulation of CEACAM6 protein expression.
The present inventor has demonstrated the inability of CEACAM1 to bind CEACAM6. The present inventor has also directly shown that the presence of both residues 43R and 44Q in the CEACAM1 is crucial for the homophilic CEACAM1 interaction and that substitution of these residues with the 43S and 44L residues that are present in CEACAM6 abolishes the inhibitory effect. The reciprocal substitution of 43S and 44L of CEACAM6 to the 43R and 44Q residues, respectively, results in the gain of inhibitory heterophilic interactions with the CEACAM1 protein. The dichotomy of CEACAM family members by recognition of CEACAM1 is determined by the presence of R and Q at positions 43 and 44.
Natural killer (NK) cells belong to the innate immune system and efficiently kill virus-infected and tumor cells. NK killing is generally restricted mainly to cells that have lost class I MHC expression, a phenomenon known as the missing self. NK cell cytotoxicity is tightly regulated by various inhibitory class I MHC-recognizing receptors. The inhibitory signal is delivered via the immuno-receptor tyrosine-based inhibitory motif (ITIM) sequences found within the cytosolic tail of these receptors. Families of class I MHC binding inhibitory receptors include members of the Ig superfamily, namely killer Ig-related two-domain long-tail (p58) and three-domain long-tail (p70) receptors, the C-type lectin complex CD94/NKG2A, and the leukocyte Ig-like receptor (Ig-like transcript) family.
There are also other NK-specific receptors, termed natural cytotoxicity receptors (NCRs), which are directly involved in triggering NK cell cytotoxicity. The NCR group consists of several proteins, including NKp30, NKp44, NKp46, NKp80, and CD16. The cellular lysis ligands for all the NCRs have yet to be identified. A viral ligand (hemagglutinin) was shown to interact with the NKp46 receptor, and this interaction resulted in the enhancement of lysis of certain virus-infected cells. Indeed, the killing activity of target cells by human natural killer (NK) cells is mediated via a panel of lysis receptors of which is included CD16, NKp30, NKp44, NKp46, and NKG2D. These receptors recognize viral ligands such as hemagglutinin, stress-induced ligands such as MHC class I chain—related antigen A (MICA) and MICB, or other as-yet-undefined, cellular ligands. As mentioned, cells are protected from lysis by NK cells mainly owing to the interactions between class I MHC proteins and the appropriate inhibitory NK receptors.
The present inventor has identified a novel class I MHC-independent inhibitory mechanism of human NK cytotoxicity, mediated via the carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) homophilic interactions. Furthermore, the present inventor has found that the CEACAM1 protein plays a pivotal role in the inhibition of killing, proliferation, and cytokine secretion of interleukin 2 (IL-2)-activated decidual NK, T, and NKT cells, respectively.
Once class I MHC proteins are removed from the cell surface, these cells become susceptible to NK cell attack. It was surprising to learn that patients with transporter associated with antigen processing (TAP2) deficiency do not frequently suffer from autoimmune manifestations at early stages of their life. Activated NK cells derived from such patients may either be expressing an unknown inhibitory mechanism or are missing an unidentified lysis receptor. NK tolerance toward self-cells might be controlled by similar mechanisms.
The present inventor has demonstrated that the expression of the NKp46 receptor is severely impaired in a newly identified TAP2-deficient family and that the vast majority of activated NK cells derived from these patients use the CEACAM1 protein interactions to avoid tumor and autologous cell killing.
The present inventor has also found that CD16-negative NK clones inefficiently kill 1106mel cells because of the CD66a homotypic interactions The inhibition of NK cell cytotoxicity by CD66a was dependent on the level of CD66a expression on both effector and target cells. 721.221 cells expressing CD66a protein were protected from lysis by CD66a-expressing NK and YTS cells. Redirected lysis experiments performed by the present inventors showed that the strength of the inhibition is dependent on the level of CD66a expression on NK cells. A dramatic increase in CD66a expression was observed among NK cells isolated from melanoma patients. As stated above, a novel class I MHC-independent inhibitory mechanism of human NK cell cytotoxicity has been demonstrated by the present inventors. Some melanoma tumors may use this mechanism to avoid attack by NK cells.
Human natural killer (NK) cells are able to eliminate a broad spectrum of tumors and virus-infected cells by using several receptors, such as CD16, NKp30, NKp44, NKp46 and NKG2D. These receptors recognize either viral ligands, such as hemagglutinin, stress induced ligands, such as MICA and MICB, or other yet-undefined cellular ligands. Other NK receptors mediate inhibition of the killing activity following interaction with MHC class I proteins present on normal cells. Removal of MHC class I proteins from the cell surface renders it susceptible to NK cell attack through the phenomenon known as the “missing self”.
Additional receptors are also able to manipulate NK cell cytotoxicity and the present inventors have shown a novel MHC class I independent inhibitory mechanism of human NK cytotoxicity that is mediated by the CEACAM1 homophilic interactions. This CEACAM1-mediated inhibition might play an important role in the in vivo development of melanoma in human patients. A 10-year follow-up study correlated the presence of CEACAM1 on primary melanoma lesions with poor survival. In addition, the present inventors have demonstrated the pivotal role of the CEACAM1 in the inhibition of killing, cytokine secretion and proliferation of activated decidual NK, NKT and T cells, respectively. The present inventors have also provided substantial evidence for a major role of the inhibitory CEACAM1 interactions in controlling NK cell autoreactivity in TAP2-deficient patients.
The presence of human soluble CEACAM1 protein can be observed in the serum of healthy donors. Furthermore, variations in serum levels of the soluble CEACAM1 protein are observed in various pathologies. For example, increased CEACAM1 levels were observed in the sera of patients with various hepatic diseases such as obstructive jaundice, primary billiary cirrhosis, autoimmune hepatitis and cholangiocarcinoma. A decrease in the soluble CEACAM1 level has not been reported.
The present inventor has shown that the soluble CEACAM1 protein blocks the CEACAM1-mediated inhibition of NK cell killing activity in a dose-dependent manner. Moreover, the present inventors have demonstrated that serum CEACAM1 levels among the TAP2-deficient patients are decreased when compared to normal individuals. These findings concur with the dominant role of the CEACAM1-mediated inhibition in controlling NK autoreactivity in TAP2-deficient patients. Thus, the maximal compensatory effect of CEACAM1-mediated inhibition is attained.
At least one object of the present invention is the modulation of CEACAM1 activity to effect control over the immune system and in particular specific immune responses in the treatment of disease. In particular, the present invention relates to the supression of specific immune responses, by increasing the functional concentration of the CEACAM1 protein, to create a protective immunity in the treatment of certain disease states, including but not limited to autoimmune diseases and diseases requiring the transplantation of tissue.
Autoimmune disease results when the immune system mistakes self tissues for nonself and mounts an inappropriate attack. There are many different autoimmune diseases. Autoimmune disease can affect many parts of the body, including but not limited to nerves, muscles, the endocrine system (system that directs your body's hormones and other chemicals), and the digestive system. Some examples are Wegener's granulomatosis, multiple sclerosis, type 1 diabetes mellitus, rheumatoid arthritis, and Crohn's disease.
Transplant rejection occurs when the immune system of the recipient of a transplant attacks the transplanted organ or tissue. This is because a normal healthy human immune system can distinguish foreign tissues and attempts to destroy the transplant, just as it attempts to destroy infective organisms such as bacteria and viruses.
At present, regimens to treat both autoimmune diseases and tissue transplant rejection employ general immunosuppressant drugs. The present invention relates to the supression of immune responses in a specific fashion, by increasing the functional concentration of the CEACAM1 protein in a target tissue to create a localized protective immunity for the treatment of autoimmune diseases and diseases requiring the transplantation of tissue.